Two-way information transmission system, two-way information method, and subscriber terminal device

ABSTRACT

A subscriber terminal ms sends a demand including at least information for identifying the demand subscriber terminal, information for identifying the requested information, and information relating to the urgency of the requested information to the information distribution transmission center HE through a going-up line. The information distribution transmission center HE plans and transmits information requested according to the transmission schedule of the information based on the demand, and transmits the transmission schedule information in the going-down control data to the subscriber terminal which sent the demand prior to the actual transmission, and transmits the requested information according to the above-mentioned transmission schedule. The subscriber terminal ms receives and analyzes the going-down control data from the information distribution transmission center HE and is informed of the transmission schedule, and acquires the information to be transmitted based on the obtained transmission plan. The subscriber terminal stores the information in a large scale memory, and reads the information from the memory for use. After the information is read from the memory for use, an information reusing disabling unit disables the reusing of the information in such a way as to delete the corresponding information from the memory.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a two-way information transmission system suchas video on-demand system and information on-demand system using acommunication network such as a cable television network.

2. Description of Related Art

Not only usual analog broadcasting service but also video on-demand,home shopping, and television game service utilizing a two-way cabletelevision network have been recently planned.

One method for realizing such services is a method in which a digitalinformation transmission band is provided, for example, in thetransmission band of the television network separately from the band foranalog broadcasting service. In detail, for example in the case of videoon-demand system, a user transmits a demand signal (transmission requestsignal) of the video on-demand to a cable television station where avideo program storing sending system called the video server isinstalled using a portion of the digital information transmission band.Upon receiving the demand signal from the user, the cable televisionstation takes out the program requested by the user from the videoserver, and provides it to the requesting user in real-time using a bandother than that for the above-mentioned demand signal in theabove-mentioned digital information transmission band.

One of such video on-demand systems is introduced in a journal “NikkeiElectronics” issued May 23, 1994 on pages 82 to 89.

This example involves a hybrid network system comprising combinedoptical fiber and coaxial cable, the optical fiber connects from thecable television station to an optical fiber node, the optical fibernode performs photoelectric conversion, and the coaxial cable connectsfrom the optical fiber node to a subscriber terminal called a set topbox installed in the user home. Assuming that 16 optical fiber nodes areprovided and the maximum number of subscribers connectable to a coaxialcable is 500, then one cable television station can supply to 8000subscribers.

In the assignment of a transmission band of the cable television, thisvideo on-demand system assigns the band range from 50 MHz to 723 MHz toa transmission band for going-down from the cable television station toa subscriber terminal of a subscriber, and the band range from 900 MHzto 1 GHz to a transmission band for going-up from a subscriber terminalto the cable television station, further, a transmission band between 50MHz to 450 MHz out of the going-down transmission band is used for theexisting analog broadcasting service and a transmission band between 500MHz to 708 MHz is used for the digital transmission band. The residualtransmission band ranging from 450 MHz to 500 MHz is a spare as shown inFIG. 1.

At most 15 digital transmission channels with a band width of 12 MHz canbe provided in the digital information transmission band ranging from500 MHz to 708 MHz. Assuming that the transmission speed per one channelis 45 M bits/sec and, for example, the coding speed of video data is 4 Mbits/sec, video data can be supplied to about 10 subscribers by way of achannel with the transmission speed of 45 M bits/sec in real-time.

Assuming that the proportion of requesting subscribers on demand to the500 subscribers is 25% in the busy time called prime time, it isrequired to supply to 125 subscribers, and one channel can supply to 10subscribers, therefore 15 channels can supply to 150 subscribers andthus the requirement is satisfied.

In the case of this example, the control channel is assigned near thefrequency of 500 MHz, and the going-down channel to be used forsupplying video program data desired by a user on demand is informed bythe set top box using this control channel. The set top box fetches onlydesired going-down data in the cable television station based on thedata of the control channel, and functions to display it on atelevision. The transmission speed of the control channel is 1.5 Mbits/sec, and 45 channels and 1 channel are for going-up and forgoing-down respectively.

FIG. 2 shows how the transmission capacity of a going-down line isallocated to respective subscribers, the left half of the figure showsso-called prime time and the right half shows the midnight time zone.

In FIG. 2, the top half shows the transmission channels for analogtelevision broadcasting service, each long rectangle represents oneanalog television program PGa. In this case, 50 channels of analogtelevision broadcasting service are possible to be transmitted if onechannel has a band width of 6 MHz. Each subscriber can select and view adesired program from programs being broadcasted by way of analogchannels any time.

The bottom half of FIG. 2 shows the digital information channels forvideo on-demand, an arrow Tdn represents a demand generating time pointfrom a user, and a long rectangle represents a one digital video programPGd. In response to a demand from a user, one channel is occupied by theuser for a time of the service.

Since charging always for real-time transmission is generally performedin case of video on-demand, the charged rate does not vary according totime zones, but is often constant. As shown in FIG. 2, therefore inprime time, the audience rating of analog broadcast programs is high andalso many demands for digital video programs are generated. On the otherhand, late at night, the audience rating of analog TV broadcast programsis low and few demands for digital video programs are generated.

As described hereinbefore, in the conventional video on-demand system,video programs are supplied in real-time to all the demands. Therefore,in the time zone like so-called prime time when many demands arerequested from subscribers, many programs should be transmitted at atime as shown in the left side of FIG. 2.

For construction of a video on-demand system, the network capacity andtransmission system are deployed so that programs are supplied tosubscriber homes as soon as possible in real-time in the busiest timezone when many demands are requested.

To cope with such a situation, the conventional system is involved in aproblem that {circle around (1)} the network capacity should be large,and {circle around (2)} the scale of video server should be large inorder to supply many programs simultaneously (for example, assuming thenumber of subscribers is 8000 and 25% of these subscribers request theirdemand in prime time, the simultaneous transmission stream are 2000streams). The capacity investment for enlargement of an existingfacility is required, and an expensive large scale video server shouldbe introduced, these expenditures can render the business substantiallyunprofitable.

As described herein above, many demands are generated frequently inprime time, on the other hand, a few demands are generated sporadicallyin the time zone of early morning and midnight. The problem isinefficient use of the network facility having a large capacity deployedso as to match with busy demand in prime time, and the capacityutilization ratio is low.

The applicant has proposed a new two-way information transmission systemfor solving problems described herein above.

In a new two-way information transmission system, not only real-timeinformation transmission, but also delayed information transmissionservice are specified in advance, memory with a large capacity isprovided for the user terminal (subscriber terminal) to storeinformation transmitted to the memory, and the user can read informationfrom the memory and use it at a desired time.

When information is stored in the memory of the subscriber terminal andthe user is permitted to freely use the stored information, however,there is a problem on the copyright of the information.

It is an object of the present invention to solve the problem of thecopyright in the above-mentioned new two-way information transmissionsystem.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problem, the two-way informationtransmission system of the present invention comprising:

an information distribution transmission center and a plurality ofsubscriber terminals connected to an information distributiontransmission center through going-up lines and going-down lines, thesubscriber terminal requesting an information from the informationdistribution transmission center through the going-up line, and theinformation distribution transmission center transmitting the requestedinformation in response to the request for the transmission;

the subscriber terminal having;

distribution transmission request sending means for sending theinformation distribution transmission request including at leastinformation for identifying the demand subscriber terminal, informationfor identifying the requested information, and information relating tourgency of the requested information,

memory means,

transmission plan receiving analysis means for being informed of thetransmission plan based on the going-down control data from theinformation distribution transmission center,

information acquisition means for acquiring the information transmittedfrom the information distribution transmission center based on thetransmission plan and storing the acquired information in the memorymeans according to the urgency of the information transmission, whichinformation was acquired by the transmission plan receiving analysismeans,

reading means for reading the information from the memory means, and

information reusing disabling means for disabling the reusing of theinformation read from the memory means by the reading means and used.

The information distribution transmission center has a;

transmission planning means for planning a transmission plan to transmitthe information based on an information distribution transmissionrequest from the subscriber terminal,

transmission implementation means for implementing the transmission ofthe requested information based on the transmission plan planned by thetransmission planning means, and

going-down control data sending means for sending going-down controldata including information involving the transmission implementationplan planned by the transmission implementation means to the subscriberterminal which sent the information distribution transmission requestbefore the transmission implementation means implements thetransmission.

In the two-way information transmission system with the above-mentionedconfiguration, the information transmission center implementsinformation transmission to the subscriber terminal not only in realtime, but at a specified delayed time in response to the transmissionplan made by the subscriber based on the information on the urgency ofinformation transmission which is the information at a desired timeincluded in a transmission request of the subscriber terminal. Thesubscriber terminal stores the transmitted information in the memorymeans and fetches the information from the memory means at a desiredtime, thus enabling the use.

Further, the information reusing disabling means, after information isread from the memory means and used, disables the reusing of theinformation. The method for disabling the reusing of information isthat, after information is read and used, the information reusingdisabling means automatically deletes the information or logicallywrites information on reusing disabling in the memory area for the readand used information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for describing an example of transmission frequencyband assignment in a two-way information transmission system.

FIG. 2 is a diagram for illustrating the use of going-down informationtransmission channels in the conventional video on-demand system.

FIG. 3 is a diagram for illustrating an example of a network structureof one embodiment of the two-way information transmission system inaccordance with the present invention.

FIG. 4 is a diagram for illustrating an example of a cable televisionstation structure as an information transmission center in oneembodiment of the two-way information transmission system in accordancewith the present invention.

FIG. 5 is a block diagram for illustrating a partial structure of thecable television station facility shown in FIG. 4.

FIG. 6 is a block diagram for illustrating an interchanging equipment inone embodiment of the two-way information transmission system inaccordance with the present invention.

FIG. 7 is a block diagram for illustrating an interchanging equipment inone embodiment of the two-way information transmission system inaccordance with the present invention.

FIG. 8 is a block diagram for illustrating a structural example of asubscriber terminal in one embodiment of the two-way informationtransmission system in accordance with the present invention.

FIG. 9 is a block diagram for illustrating a partial structure of thesubscriber terminal shown in FIG. 8.

FIG. 10 is a functional block diagram of a selected portion forillustrating one embodiment of the two-way information transmissionsystem in accordance with the present invention.

FIG. 11 shows an example of the table of charges for transmission in oneembodiment of the two-way information transmission system of the presentinvention.

FIG. 12 is a diagram for illustrating the use of the going-downtransmission channels in one embodiment of the two-way informationtransmission system in accordance with the present invention.

FIG. 13 is a flowchart for describing an example of demand transmissionprocessing from a subscriber terminal in one embodiment of the two-wayinformation transmission system in accordance with the presentinvention.

FIG. 14 shows an example of part of the input screen on demand in oneembodiment of the present invention.

FIG. 15 is a flowchart for describing an example of demand receivingprocessing in a cable television station in one embodiment of thetwo-way information transmission system in accordance with the presentinvention.

FIG. 16 is a flowchart for describing an example of receiving processingof going-down digital transmission data at a subscriber terminal in oneembodiment of the two-way information transmission system in accordancewith the present invention.

FIG. 17 is a flowchart for describing an example of information readingprocessing at a subscriber terminal in one embodiment of the two-wayinformation transmission system in accordance with the presentinvention.

FIG. 18 is a flowchart for describing an example of reproduction requestreceiving processing in a cable television station in one embodiment ofthe two-way information transmission system in accordance with thepresent invention.

FIG. 19 is a diagram for describing an example of the network structurein another embodiment of the two-way information transmission system inaccordance with the present invention.

FIG. 20 is a diagram for describing an example of transmission frequencyband assignment in another embodiment of the two-way informationtransmission system in accordance with the present invention.

FIG. 21 is a block diagram for illustrating a structural example of acable television station in another embodiment of the two-wayinformation transmission system in accordance with the presentinvention.

FIG. 22 is a block diagram for illustrating a structural example of asubscriber terminal in another embodiment of the two-way informationtransmission system in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the two-way information transmission system in accordancewith the present invention will be described in detail referring to thedrawings for the example of a video on-demand system. The direction froma subscriber to a cable television station is referred to as going-up,and the inverse direction is referred to as going-down in thedescription hereinafter.

FIG. 3 shows the outline of a network structure used for realizing avideo on-demand of an embodiment of the two-way information transmissionsystem. This example has the same structure as that of the two-way cabletelevision system described in the chapter of related art.

The cable television station HE called head end provides analogtelevision broadcast programs always during the broadcasting time zoneand also video programs in response to the demand from subscribers andother programs.

The cable television station HE can cover, for example, 8000 subscribersas described herein above, 8000 subscribers are divided into 16 sectionsand each section covers 500 subscribers MS. Interchange equipment IMcalled an optical fiber node (referred to as optical fiber node IMhereinafter) is installed for each section. An optical fiber node IMperforms mutual conversion between an optical signal and an electricsignal.

In the case of this embodiment, an optical fiber cable FB connectsbetween each section and the television station HE in order to transmita signal without degrading in quality across a long distance. In eachsection, one coaxial cable CB is connected to an optical fiber node IM,and each subscriber MS is connected to the coaxial cable through acoaxial confluent distributor MPX. At most 500 subscribers MS areconnectable to one coaxial cable CB as described hereinbefore.

The cable television station HE has information sources including avideo server, and is connected to an optical fiber trunk SHW in order tofetch digital information from the optical fiber trunk SHW and provideit to the subscribers in addition to digital data from the digitalinformation source of the cable television station HE itself. Further, aparabola antenna AT is provided for receiving satellite broadcast, andreceived television broadcast is supplied to respective subscribers asanalog television broadcast.

FIG. 4 shows an example of facility components of the cable televisionstation HE, and in this example, the facility comprises theabove-mentioned analog television broadcasting facility not shown inFIG. 4, for example video server 21 and tape information library system22 as a digital information source equipment, high speed ATM(non-synchronous transfer mode) exchanger 23, HE controller 24 forcontrolling the whole system of the cable television station HE, and 16node controllers 25 a to 25 p provided between 16 respective opticalfiber cables FB and ATM exchangers.

In this example, the video server 21 obtains, for example, 400 streamsas a bit stream of a simultaneous transmission video signal. The codingrate of each bit stream data is, for example, 4 M bits/sec, and, forexample, MPEG is used as a data compression system. In this case, twovideo servers may be provided as the video server 21 if, for example,simultaneous transmission stream quantity is 200 streams. Data VA ofeach video stream from the video server 21 is supplied to ATM exchanger23.

The tape information library system 22 is provided with a multi-shelfcontainer rack 22L in which many video tapes are placed on respectivelyspecified positions, a plurality of video tape players VTR1 to VTRn, anda retrieving transferring mechanism (not shown in the figure) which issuccessively operated for retrieving in the horizontal and verticaldirection to find out the position of a requested video tape in thecontainer rack 22L, for fetching the video tape, setting the video tapeinto any one of video tape players VTR1 to VTRn to playback the videotape, such tape information library system 22 is called a as cartmachine. In this example, 160 video tape players are deployed.Therefore, the number of bit streams of the simultaneous transmissionvideo signal is 160.

Data VB of the digital video data stream of respective video tapeplayers VTR1 to VTRn has a transmission rate of, for example, 45 Mbits/sec. The data VB is supplied to the ATM exchanger.

The tape information library system 22 provides more programs and iseasier than the video server 21.

The HE controller 24 controls the whole cable television station HEincluding the control of the video server 21, control of the tapeinformation library system 22, and control of the ATM exchanger 23,generates going-down control data DM to be transmitted to a subscriberand supplies it to the ATM exchanger 23 in response to an operationinput from an operator to the HE controller 24 and going-up control dataUM (data such as a demand signal of the video on-demand) from asubscriber terminal supplied through the ATM exchanger 23.

Also digital data VC obtained from the optical fiber trunk SHW issupplied to the ATM exchanger 23.

The ATM exchanger 23 exchanges the above-mentioned digital data VA, VB,and VC, and going-down control data DM and divides or gathers them togenerate information necessary for respective transmission sections. TheATM exchanger 23 also transfers a going-up control data UM from asubscriber terminal to the HE controller 24.

Respective 16 node controllers 25 a to 25 p receive the analogtelevision broadcast signal AV and going-down information from the ATMexchanger 23, and convert them to a signal having the frequency bandpreviously assigned and convert an electric signal to a light signal,and send it to the optical fiber FB as described in FIG. 1. Therespective 16 node controllers 25 a to 25 p convert going-up controldata UM from a light signal to an electric signal, and transfer it tothe ATM exchanger 23.

All node controllers 25 a to 25 p have the same structure. FIG. 5 is ablock diagram for illustrating the structure of one node controller outof the node controllers 25 a to 25 p. The optical fiber FB comprisesthree optical fibers fb1, fb2, and fb3.

The analog television information AV is supplied to a band pass filter102 through an input terminal 101, and converted to information having afrequency band of 50 MHz to 450 MHz, and supplied to theelectric-to-light converter 103.

The electric-to-light converter 103 converts it to a light signal andsends it to the optical fiber fb1.

In this example, as shown in the above-mentioned FIG. 1, 15 channels areallocated for the going-down digital transmission data of 45 M bits/secper one channel. Therefore, the node controller has 15 digitaltransmission data input terminals 104 ₁ to 104 ₁₅. The ATM exchanger 23switches directly the digital data such as a video stream from the tapeinformation library system 22 to any one of 15 input terminals 104 ₁ to104 ₁₅ of a node controller corresponding to the section of theaddressee subscriber.

The ATM exchanger 23 switches digital data of 4 M bits/sec bit streamfrom the video server 21 in a manner that at most 10 streams aremultiplexed and allocated to one channel.

Respective 45 M bits/sec digital data transmitted through the inputterminals 104 to 104 are supplied to hexternal QAM (Quadrature AmplitudeModulation) modulation circuits 105 ₁ to 105 ₁₅ respectively andmodulated. The output data from the hexternal QAM modulation circuits105 ₁ to 105 ₁₅ is converted by the frequency conversion circuits 106 ₁to 106 ₁₅ respectively to signals of 15 channels which are signals of 15frequency bands not superposing each other in the frequency band rangingfrom 500 MHz to 708 MHz as shown in FIG. 1. The output data from thefrequency conversion circuits 106 ₁ to 106 ₁₅ is supplied to the addingcircuit 107 and the frequency of the data is converted.

A node controller has an input terminal 110 for receiving 1.5 M bits/secgoing-down control data DM of one channel. The control data DM whichpassed through the input terminal 110 is supplied to QPSK (QuadraturePhase Shift Keying) modulation circuit 112 through the multiplexingcircuit 111, and subjected to QPSK modulation, and then supplied to afrequency conversion circuit 113 and converted to a signal of thegoing-down control channel near 500 MHz shown in FIG. 1. Subsequently,the signal is supplied to the adding circuit 107 and subjected tofrequency multiplexing.

The frequency multiplexed data from the adding circuit 107 is suppliedto the band pass filter 108 and subjected to band restriction to asignal in a frequency band ranging from 500 MHz to 708 MHz, and suppliedto the electric-to-light converter 109. The electric-to-light converter109 converts it to a light signal, and sends it to the optical fiber fb2as digital transmission data.

The optical fiber fb3 is used for the going-up control channel, agoing-up control signal such as a demand of a subscriber which is QPSKmodulated and includes 45 channels by frequency multiplexing is suppliedto a light-to-electric converter 121 through the optical fiber fb3, andthe signal is converted from a light signal to an electric signal. Theoutput signal from the light-to-electric converter 121 is supplied to aband pass filter 122 and subjected to the band restriction, and thenonly the going-up control data having a frequency band ranging from 900MHz to 972 MHz is fetched.

The control data from the band pass filter is supplied to 45 frequencyconversion circuits 123 ₁ to 123 ₄₅ corresponding to frequency bands of45 channels and subjected to frequency conversion, the frequencyconverted data is processed as modulation data for respective channels.The modulation data for each channel from the frequency conversioncircuits 123 ₁ to 123 ₄₅ is demodulated in a QPSK demodulation circuit124 ₁ to 124 ₄₅ to control data of 1.5 M bits/sec. The control data issubjected to time slicing multiplexing in the multiplexing circuit 111,and it is sent to the ATM exchanger 23 through an output terminal 125 asgoing-up control data UM.

Next, the structure of the optical fiber node IM is described. FIG. 6 isa block diagram of an example of an optical fiber node.

A light-to-electric converter 201 receives an analog television signalthrough the optical fiber fb1 for the analog television broadcast lineand converts it to an electric signal, and thereafter supplies it to aband pass filter 202. The band pass filter 202 fetches only an analogtelevision signal in a frequency band ranging from 50 MHz to 450 MHzfrom the input signal, and supplies it to an adding circuit 203.

A light-to-electric converter 204 receives going-down digitaltransmission data of 15 channels through the optical fiber fb2 andconverts it to an electric signal, and supplies it to a band pass filter205. The band pass filter 205 fetches only digital transmission data ina frequency band ranging from 500 MHz to 708 MHz from the input data,and supplies it to the adding circuit 203.

The adding circuit 203 adds the analog television broadcast signal anddigital transmission data for frequency multiplexing, and supplies thefrequency multiplexed signal to a band pass filter 207 through anamplifier 206. The band pass filter 207 performs band restriction within50 MHz to 708 MHz on the input signal, and thereafter sends thefrequency multiplexed signal to the coaxial cable CB.

Data sent from a subscriber terminal through the coaxial cable CB issupplied to a band pass filter 208. The band pass filter 208 performsband restriction within 900 MHz to 972 MHz on the input data and fetchesgoing-up control data, and supplies it to an electric-to-light converter210 through an amplifier 209. The electric-to-light converter 210converts the going-up control data to a light signal and sends it to theoptical fiber fb3.

Next, a structural example of a coaxial confluent distributor MPX isdescribed referring to FIG. 7. In detail, going-down line data from thecoaxial cable CB of the optical fiber node IM side is supplied to a bandpass filter 211. The band pass filter 211 performs band restriction onthe input signal within a band ranging from 50 MHz to 708 MHz, andsupplies it to a distributor 212.

The distributor 212 supplies the going-down line data to a subscriberterminal connected to the coaxial confluent distributor MPX. Also, thedistributor 212 supplies the going-down line data to a band pass filter214 through an amplifier 213. The band pass filter 214 performs bandrestriction on the going-down line data for down-stream subscriberswithin a frequency band ranging from 50 MHz to 708 MHz, and sends it tothe coaxial cable CB.

Data from the down-stream side coaxial cable CB is supplied to a bandpass filter 215. The band pass filter 215 performs band restriction onthe input data within a frequency band ranging from 900 MHz to 972 MHzto allow the going-up control data to pass, and supplies it to asynthesis circuit 216. The synthesis circuit 216 adds the going-upcontrol data from down-stream subscribers and the going-up control datafrom the subscriber connected to the coaxial confluent distributor MPX,and supplies the synthesized data to a band pass filter 218 through anamplifier 217. The band pass filter 218 performs band restriction on theinput data within a frequency band ranging from 900 MHz to 972 MHz andsends it to the up-stream coaxial cable CB.

The frequency band for control data of respective subscribers ispreviously assigned so as not to overlap each other in one section.

Next, a structural example of a subscriber terminal ms provided in asubscriber's house MS is described referring to FIG. 8 and FIG. 9.

In detail, going-down channel data from the coaxial confluentdistributor MPX is fed to an input terminal 301. Going-up control datais sent from an output terminal 302 to the coaxial confluent distributorMPX. The coaxial input terminal 301 and coaxial output terminal 302 areconnected to a demodulation/modulation unit.

The demodulation/modulation unit 303 has the structure shown in FIG. 9.In detail, going-down line data from the coaxial input terminal issupplied to a band pass filter 304. The band pass filter 304 extracts ananalog television broadcast signal in a frequency band ranging from 50MHz to 450 MHz and supplies it to a frequency conversion circuit 305.

The frequency conversion circuit 305, which corresponds to a mixercircuit of a tuner, converts a signal of the broadcast program(broadcast channel) selected by a user out of received analog televisionbroadcast signals to a signal having a frequency which can bedemodulated by a subsequent analog television demodulation circuit 306in response to a channel select control signal corresponding to achannel select operation of the user supplied from a terminal controller320 described hereinafter, and supplies it to an analog televisiondemodulation circuit 306. The demodulation circuit 306 supplies thedemodulated television signal to a television through a switch circuit315 and video output terminal 316 shown in FIG. 8.

Further, going-down line data from the coaxial input terminal 301 issupplied to a band pass filter 307. The band pass filter 307 extractsgoing-down digital data having a frequency in the band ranging from 500MHz to 708 MHz and supplies it to a frequency conversion circuit 308 andfrequency conversion circuit 309.

The frequency conversion circuit 308 converts only the signal of thechannel to which a video program delivered in response to the demandfrom the demand subscriber terminal based on a channel select controlsignal from the terminal controller 320 to a prescribed frequency whichcan be demodulated. Digital transmission data such as video program dataaddressed to the demand subscriber terminal from the frequencyconversion circuit 308 is supplied to a hexternal QAM demodulationcircuit 310 and demodulated. The 45 M bits/sec digital data from thedemodulation circuit 310 is supplied to the de-multiplexing circuit 317.

The frequency conversion circuit 309 frequency-converts the frequency ofcontrol channel data assigned previously to the demand subscriberterminal to a frequency which can be demodulated based on a channelselect control signal from the terminal controller 320. The going-downcontrol data from the frequency conversion circuit 309 is supplied to aQPSK demodulation circuit 311 and demodulated. The 1.5 M bits/seccontrol data from the demodulation circuit 311 is supplied to thede-multiplexing circuit 317.

A QPSK modulation circuit 312 of the demodulation/modulation unit 303receives going-up control data, which will be described hereinafter,through the de-multiplexing circuit 317, and modulates it, and suppliesit to a frequency conversion circuit 313. The frequency conversioncircuit 313 frequency-converts the frequency of the input signal to afrequency of the control channel assigned to the demand subscriberterminal in a frequency band ranging from 900 MHz to 972 MHz. Thegoing-up control data from the frequency conversion circuit 313 is sentto the coaxial cable CB through a band pass filter 314 for bandrestriction within 900 MHz to 972 MHz and through the output terminal302.

The de-multiplexing circuit 317 extracts 4 M bits/sec digitaltransmission data addressed to the demand subscriber terminal from 45 Mbits/sec output data supplied from the hexternal QAM demodulationcircuit 310 based on the control signal from the terminal controller 320if the digital transmission data is 4 M bits/sec immediate real-timetransmission data, and supplies it to a digital television signaldecoding circuit 319 through a switch circuit 318.

The switch circuit 318 receives a switching control signal from theterminal controller 320, selects digital data from the de-multiplexingcircuit 317 during real-time transmission, and selects the read data asan output and supplies the data to the digital television signaldecoding circuit 319 when data is read from the temporary memory meansin response to a reading request inputted by the user.

The digital television signal decoding circuit 319 decodes the digitaldata and converts it to an analog television signal, and supplies theanalog television signal to a television through the switch circuit 315and video output terminal 316.

In the embodiment, the digital television signal decoding circuit 319 isprovided with the circuit section for removing copying prohibitingprocessing of the information to be transmitted for which copyingprohibiting processing is specified to enable the copying of theinformation transmitted in real time or the information stored in thetemporary memory means 330, as described later, when the user makes arequest for removing copying prohibiting processing of the information.

The control signal for removing the copying prohibiting processing issent from the cable television station through the going-down controlline. Then, the terminal controller 320 receives the control signal forremoving the copying prohibiting processing and transfers the controlsignal to the digital television signal decoding circuit 319 to make thecircuit 319 remove the copying prohibition processing. In this case,processing applied to recording information of a currently availablevideo cassette tape is used as the copying prohibiting processing.

The de-multiplexing circuit 317 sends the digital transmission datawhich is to be transmitted to the demand subscriber terminal to thetemporary memory means 330 and stores it temporarily in the case thatthe digital transmission data is delaying transmission data referring tocontrol data from the terminal controller 320. In this case, thedelaying transmission data may be at a 4 M bits/sec rate or 45 Mbits/sec rate as described hereinafter.

A semiconductor memory 331 which is a data memory device having a largecapacity (about 1 G bits) and high speed transmission rate, hard diskdevice 332 (about 10 G bits), or data streamer 333 (about 200 G bits) isused as the temporary memory means 330. The temporary memory means 330has such a mechanism that the memory medium such as a semiconductormemory, disk, or tape cannot directly be removed from the outside, thatis, from the inside of the body of the subscriber terminal. In otherwords, for example, the entire temporary memory means 330 is containedin a shielded cabinet. Or, devices 331, 332, and 333 are containedrespectively in different cabinets and so structured that each memorymedium cannot be removed.

In the embodiment, the user cannot issue a write (record) instructionand a read (reproduce) instruction to respective devices 331 to 333 ofthe temporary memory means 330 directly via the interface 321, but suchinstructions can be issued under the control from the cable televisionstation.

According to a storing instruction issued from the cable televisionstation through the terminal controller 320, the digital transmissiondata from the de-multiplexing circuit 317 is therefore stored in thetemporary memory means 330, while, according to a reading instructionissued from the cable television station through the terminal controller320, the stored data is read, and the read data is supplied to thedigital television signal decoding circuit 319 through the switchcircuit 318.

In this case, as described hereinafter, the terminal controller 320determines which memory means is to be selected among the plurality ofmemory means of the temporary memory means 330 as the memory for storingthe going-down digital data depending on the random access potential andtransmission format (such as data transmission rate) of the digital datato be stored which are specified by the going-down control data ordetermined by the demand sent by the demand subscriber terminal.

For example, if the data transmission rate is 4 M bits/sec and the datahas a low random access potential such as usual video program, then thedata is stored in the data streamer device 333 which uses tapes as therecording medium, on the other hand, if the data has high random accesspotential such as stock market information, then the data is stored inthe hard disk device 332, and if the data is a transmission data with adata transmission rate of 45 M bits/sec, then the data is written in thesemiconductor memory 331 capable of high speed writing, as describedherein. The memory means in which data is to be stored is controlled andselected.

The de-multiplexing circuit 317 supplies going-down control data fromthe QPSK demodulation circuit 311 to the terminal controller 320 bycontrolling the terminal controller 320.

The terminal controller 320 analyzes the going-down control data fed tothe terminal controller 320 through the de-multiplexing circuit 317, andif the control data is addressed to the demand subscriber terminal, theterminal controller 320 generates various control signals as describedherein above based on the control data. For example, the terminalcontroller 320 acquires various information regarding when the videodata demanded by the demand subscriber terminal will be transmitted byway of what channel out of 15 going-down channels in what transmissionformat, from the received going-down control data, and prepares forreceiving. The channel select control signal to the frequency conversioncircuit 308, the control signal for multiplexing to the multiplexingcircuit 317, and the select control signal for selecting a memory devicein the temporary memory device 330 which are described herein above aregenerated from this going-down control data.

Further, the terminal controller 320 receives an operational input by auser through a user interface 321 comprising a remote control device andkey operation board, generates going-up control data, namely a demandsignal of video on-demand, and supplies it to the de-multiplexingcircuit 317. The terminal controller 320 controls the whole subscriberterminal ms.

Going-up control data such as video program demand sent from theterminal controller 320 to the de-multiplexing circuit 317 is suppliedsuccessively to the QPSK modulation circuit 312 of thedemodulation/modulation unit 303, frequency conversion circuit 313, andband pass filter 314, modulated as described hereinbefore,frequency-converted to a signal of the control channel assigned to thedemand subscriber terminal, and sent to the cable television station HE.

The de-multiplexing circuit 317 is connected to a CATV telephoneterminal (not shown in the figure) through the terminal 341 and 342,whereby subscribers can communicate with operators of the cabletelevision station HE.

The information transmission mechanism and the transmission of a signalin the two-way CATV system having the system structure as describedabove are described hereinafter.

Analog television broadcast

Analog television broadcast is transmitted from the cable televisionstation HE to subscriber terminals ms by way of one-way transmission asusual without demand from subscribers.

When a user wants to view an analog television broadcast from the cabletelevision station HE, the user operates a channel select operation forselecting an analog television broadcast of the cable television stationHE through the user interface 321 of the subscriber terminal ms. Then,the terminal controller 320 of the subscriber terminal ms supplies achannel select signal corresponding to the channel select operation ofthe user to the frequency conversion circuit 305 of thedemodulation/modulation unit 303, and the switch circuit 315 is switchedto the mode for selecting an analog television signal from the analogtelevision demodulation circuit 306 of the demodulation/modulation unit303, and thereby an analog television signal is supplied from the videooutput terminal 316 to a television. Thus the subscriber can view ananalog television broadcast program selected by the user from the cabletelevision station.

Digital information transmission

FIG. 10 is a block diagram for describing mainly functions which areperformed at the HE controller 24 of the cable television station HE andthe terminal controller 320 of a subscriber terminal ms to transmitdigital information in the system of the above-mentioned embodiment inwhich the cable television station HE and subscriber terminals ms areconnected through the going-up and going-down lines comprising opticalfibers and coaxial cables.

As shown in FIG. 10, the cable television station HE provided as aninformation distribution transmission center is connected to a pluralityof subscriber terminals ms through the going-up line Cu which is theline for transmission toward the cable television station and thegoing-down line Cd. As described above, the going-down line contains aline for program information to be transmitted and a line for thegoing-down control data.

The cable television station HE functionally comprises digitalinformation source 1, going-down information signal generator 2,information transmission control means 3, transmission planning means 4,demand receiving analysis means 5, control information generating means6, charging means 7, and authentication information and charginginformation database 8.

The digital information source 1 includes video server 21, tapeinformation library device 22, and so on. The going -down informationsignal generator 2 comprises an ATM exchanger 23 and node controllers 25a to 25 p.

The demand receiving analysis means 5 receives and analyzes the contentsof the demand from a subscriber terminal ms and passes the analyzedcontents to the information transmission control means 3 and thetransmission planning means 4. The transmission planning means 4 makes atransmission plan according to the results of the demand analysis. Thecontrol information generating means 6 generates going-down control databased on the control information from the information transmissioncontrol means 3 and the transmission planning means 4, necessaryinformation, and the information from the database 8.

The information transmission control means 3 controls the transmissionof going-down digital information and the sending of going-down controldata by controlling the digital information source 1, the going-downinformation signal generator 2, and the control information generatingmeans 6. The charging means 7 performs charging based on the results ofthe demand analysis received from the transmission planning means 4 andthe information on charging from the database 8.

The database 8 holds the authentication information for the permissionof the copying of transmission information and the table of charges tobe used when the charging means 7 performs charging.

The information transmission control means 3, transmission planningmeans 4, analysis section of the demand receiving analysis means 5, andcharging means 6 are realized as functions of the HE controller 24(realized by software).

Respective subscriber terminals ms receive the going-down control dataof their own destinations from the demand sending means 11 for sending ademand (transmission request) to the going-up line Cu, the temporarymemory means 12 with a large capacity, and the going-down line Cd, andeach subscriber terminal is provided with a transmission plan receivinganalysis means 13 for analyzing the transmission plan informationincluded in the going-down control data, a transmission informationreceiving control means 14, and a copying enabled conversion means 15.

The transmission information receiving control means 14 receives thedigital transmission data of its own destination from the going-downline Cd, demodulates the data, supplies the demodulated output to amonitor/television set, not shown, through the copying enabledconversion means 15 when real-time reproduction is required, or storesreceived transmission information of its own destination in thetemporary memory means 12 when no real-time reproduction is required.

The copying enabled conversion means 15 is a circuit section included inthe above-mentioned digital television decoding circuit 319 and, asdescribed above, removes copying prohibition processing, what is called,a copy guard applied to the video program information to be transmitted.

The demand transmission means 11 receives a demand of a user through theuser interface such as a remote controller or key board, generates adistribution transmission request signal (demand signal), and sends itto the going-up line Cu.

A demand signal includes a user ID which is an identification code ofeach subscriber, transmission program specifying information (programidentifying data) for specifying a video program requested fordistribution, request time information which is information relating tothe urgency of the requested information transmission such as the timewhen the program is desired to be transmitted or the time when thesubscriber wants to view it, and transmission format specifyinginformation for specifying whether a format of 4 M bits/sec digitalinformation or 45 M bits/sec digital information is desired.

In this case, the information of the time may be used as it is as therequest time information, however in this embodiment, several classesare defined depending on the urgency of a request, and the request timeinformation specifies a class. In detail, {circle around (1)} if a userwants to view the program immediately, then the program is demanded asA-class urgency, {circle around (2)} if a user wants to view later, thenthe program is demanded as B-class urgency, and {circle around (3)} if auser wants to view within a half or one day, then the program isdemanded as C-class urgency.

In this embodiment, a user's command via the user interface is notdirectly supplied to the temporary memory means 12 in the subscriberterminal ms, and writing (recording) and reading (reproducing) areenabled under the control of the cable television station HE. Thisprevents a free use of transmission information in the temporary memorymeans 12 to protect the copyright of the information.

When the user wants to read the video program information stored in thetemporary memory means by the user, the demand sending means 11 receivesa reading request made by the user via the user interface and sends thereading request to the cable television station HE through the going-upline Cu. The reading request includes reading request identificationdata, a user ID, and program identification data for specifying a videoprogram to be read. In this embodiment, as described later, it isdefined that the user is permitted to copy a video program, but thecopying permission request is included in the above-mentioned readingrequest.

The going-down control information receiving analysis means 13 receivesand analyzes the going-down control data sent from the cable televisionstation HE to examine whether information is transmitted in real time orbehind time, the degree of random accessibility, whether authenticationinformation used to permit copying is included in the controlinformation, and suchlike. The transmission information receivingcontrol means 14 and the copying enabled conversion means 15 arecontrolled according to the results of the analysis.

In this case, when the authentication information for copying permissionis not detected, the copying enabled conversion means 15 outputs theinput signal (real-time transmission information and the informationread from the temporary memory means 12) as it is, and copyingprohibition processing is still applied to the input signal. When theauthentication information for copying permission is detected, thecopying enabled conversion means 15 operates to remove the copyingprohibition processing of the input signal and outputs the signal. Ifthe output signal is recorded with a VTR, the signal can therefore bereproduced and used as it is.

Next, charging for information transmission is described. In thisembodiment, different charges are specified for each demand class. FIG.11 is an example of the table of charges. In this example, charges varyaccording to the periods of time when information transmission isperformed as well as demand classes. Since the information must betransmitted within the prime time when a A- or B-class demand is made inprime time, a high charge is applied to the transmission. A low chargeis applied to the transmission during midnight and early morning. Inaddition, the higher the information transmission urgency of a classdemand is, the higher charge is applied to the class demand.

When copyright fees are collected for information transmission of eachprogram, the copyright fees are included in each of the charges in theabove-mentioned table of charges. However, in the sameway as forbroadcasting, the copyright fee is charged each time a program is used.As described above, in this embodiment, it is designated that the useris permitted to copy the video program stored in the temporary memorymeans 12. In this case, however, an additional fee can be collected as acopyright fee applied during copying every time a desired video programis copied, as shown in FIG. 11.

In this example, free channels are prepared so that informationtransmission can be performed at a time other than the prime time inresponse to C-class demands and real-time information transmission canbe performed in prime time in response to A-class demands.

Charges are specified as described above to suppress the concentrationof traffic in prime time by raising the fee for information transmissionin the time zone of much traffic. Further, an appropriate additional feeis specified for copying.

In this embodiment, in the 45 MHz×15 channel transmission band for thegoing-down digital transmission data, the transmission capacity isallocated dynamically to the demand urgency classes dependently on theactual traffic condition of respective time zones in a day in order touse efficiently the transmission capacity.

For example, in a prime time zone, when many A-class demands aregenerated, the capacity is allocated as described hereinafter.

Transmission to A-class demand: 45 M bits/sec×5 channels

Transmission to B-class demand: 45 M bits/sec×8 channels

Transmission to C-class demand: No allocation

Transmission to D-class: 45 M bits/sec×2 channels

In the midnight time zone when a few demands are generated, the capacityis allocated as described herein under.

Transmission to A-class demand: 45 M bits/sec×2 channels

Transmission to B-class demand: 45 M bits/sec×2 channels

Transmission to C-class demand: 45 M bits/sec×10 channels

Transmission to D-class: 45 M bits/sec×1 channel

It is considered that many demands for video programs are requested inprime time, so that no program is transmitted to C-class demands andmore channels are allocated for transmission to A-class and B-classdemands in order to transmit programs with a waiting time as short aspossible.

Two channels are allocated to D-class transmission in order to providemany digital broadcast programs in prime time.

On the other hand, it is considered that a few demands for digitaltelevision broadcast programs are requested in the midnight time zoneand the number of broadcast programs may be not many, so that the numberof transmission channels for digital television broadcast is reduced byone channel comparing with the number in the prime time zone. It isconsidered that if fewer demands for video programs are requested in themidnight time zone than in prime time zone, then the number of channelsfor transmission to A-class and B-class demands is reduced, and moretransmission capacity and more channels are allocated to C-class demandsso that C-class demands which have been accepted previously aretransmitted.

An example of the allocation of transmission capacity for the going-downdigital transmission data allocated as described herein above is shownin FIG. 12. In FIG. 12, the abscissa represents the time, and the axisof ordinate represents the allocation of 15 channel capacity for thedigital transmission data.

An arrow ↑ represents a time point of generation of a distributiontransmission request instruction, and a section enclosed by a rectanglerepresents a program. “For broadcast” represents the transmissioncapacity for digital television broadcast, “real-time V.O.D.” representsthe transmission capacity for real-time transmission of A-class demands,“little delay V.O.D” represents the transmission capacity for digitalinformation transmission of B-class demands, and “much delay V.O.D”represents the transmission capacity for digital informationtransmission of C-class demands like the above-mentioned FIG. 2.

As shown in FIG. 12, no transmission capacity is allocated fortransmission of C-class demands in prime time. The allocated channels“real-time V.O.D” transmit in real-time in response to a demand, and theallocated channels “little delay V.O.D” transmit with little delay froma demand when looking for a free channel. The transmission time of oneprogram can be shorter than the transmission time by way of theallocated channel to “real-time V.O.D” because of 45 M bits/sectransmission in this case.

In the midnight time zone, more channels are allocated to “much delayV.O.D”, and many programs are transmitted to the previously acceptedC-class instructions which allows much delay. Accordingly, the midnighttime zone when usually a little demand is generated is used efficiently,and the transmission is performed efficiently.

Generation and transmission of distribution transmission request signal

FIG. 13 is a flowchart of a routine for generation and transmission ofdemand signals of video on-demand at a subscriber terminal.

Upon receiving a command input for sending a distribution transmissionrequest from a user through the user interface 321 in the subscriberterminal ms, the processing routine shown in FIG. 13 starts. In step S1,the user displays the operation menu for demand input. In the step, whenthe user selects the item on charges, the table of charges is displayedas shown in FIG. 14. The contents of the table are the same as those ofthe above-mentioned table of charges. The user can specify a class for ademand, referring to the displayed table.

As described above, the charge for a demand varies according to thedemand input time. In the table of charges in FIG. 14, an applied chargeis for example highlighted according to the time of the input operationof the demand. If the demand input time is in prime time, for instance,the A- and B-class fields for the prime time zone and a C-class fieldare highlighted with a double frame in FIG. 14, and the user is notifiedof the highlighted charges for the demands.

When the input by the user is accepted in step S2, it is determinedwhich class demand has been specified as request time information on theurgency of transmission. If an A-class demand is specified as requesttime information, the process proceeds to step S4, in which an A-classdemand signal is generated, and the process proceeds to step S5, inwhich it is determined whether a copying permission request is inputtedby the user. When a copying permission request is inputted in advance,the process proceeds to step S6, in which the copying permission requestis included in a demand. The process proceeds to step S9, in which thedemand signal is sent to the going-up line Cu. Unless the copyingpermission request is inputted in step S5, a jump is made to step S9, inwhich the demand excluding the copying permission request is sent to thegoing-up line Cu.

If the request time information is B-class or C-class, the processproceeds to the step S7, at which the specification of transmissionformat is judged to be either the transmission rate of the transmissiondata of 4 M bits/sec or 45 M bits/sec, and the specification of randomaccess is judged. Then, the process proceeds to the next step S8, atwhich a demand signal including the judged format, random access, andurgent class is generated, and the demand signal is sent to the going-upline Cu in the step S9.

The distribution transmission request demand signal includes a user IDfor identifying the subscriber terminal and program identifying data foridentifying a desired video program as described hereinbefore.

Receiving processing of distribution transmission request demand

FIG. 15 is a flowchart of a processing routine for receiving a demandsignal from a subscriber terminal in the HE controller 24 of the cabletelevision station HE.

Upon receiving the demand signal sent from a subscriber terminal throughthe going-up line Cu, the transmission request receiving analysis means5 of the cable television station HE transfers the request timeinformation included in the demand signal to the transmission planningmeans 4, and transfers the user ID and program identifying data to theinformation transmission control means 3. (step S11).

The transmission planning means 4 analyzes the request time information,and determines which demand class of A-class, B-class, or C-class isincluded in the request time information included in the demand signal(step S12). The determination result is reported to the charging means7.

If the request time information is determined as A-class which requestsreal-time transmission, then the transmission planning means 4 looks fora free going-down line transmission channel assigned to “for real-timeV.O.D” shown in FIG. 12, and if the transmission planning means 4 findsa free channel, the free channel is decided to be a real-timetransmission channel (step S13).

Upon receiving this decision, the information transmission control means3 informs the subscriber who sent the demand of the real-timetransmission channel (step S14). It is determined whether a demandcontains a copying permission request (step S15). When the copyingpermission request is contained in the demand, authenticationinformation for copying permission is acquired from the database 8, andthe subscriber is informed of the acquired information (step S16). Thevideo program specified by program identification data is extracted fromthe digital source 1, and real-time transmission is carried out (stepS17).

Further, the process proceeds to step S18, in which charging isperformed, and then demand receiving processing is terminated. In thiscase, charging is performed for the A-class demand included in a copyingpermission request.

As a result of the determination in step S15, if no copying permissionrequest is included in the demand, the process proceeds from step S15 tostep S19, in which the authentication information for copying permissionis not sent, but real-time information transmission is performed. Then,the process proceeds to step S20, in which charging is performed for theA-class demand that does not include a copying permission request.

At this time, the digital transmission data is fetched from the videoserver 21 and transmitted by way of the channel of the above-mentioned“for real-time V.O.D”.

If the request time information judged in the step S12 is B-class and isthe transmission request which allows a little delay, the transmissionplanning means 4 looks for a free channel from the going-down channel“for little delay V.O.D” in FIG. 12 for B-class, and decides atransmission time so as to transmit by way of the free channel (stepS21).

The transmission planning means 4 having the free channel to be used forthe transmission, transmission time, and above-mentioned analysis resultinforms the information transmission control means 3. The transmissionplanning means 4 also informs the charging means 6 of information on thetransmission time. Further, the transmission planning means 4 analyzesthe transmission format information included in the demand signal andrandom access information, and having of the analysis result informs theinformation transmission control means 3.

The information transmission control means 3 generates going-downcontrol data including the free channel, transmission time (startingtime and ending time), transmission format (4 M bits/sec transmissionrate or 45 M bits/sec transmission rate), and random access information.The going-down control data has the user ID as header information. Inaddition, the information transmission control means 3 sends thegoing-down control data to the subscriber who sent a demand specified bythe user ID, and reports the transmission time, transmission format, andso on to the terminal of the subscriber who sends the demand (step S23).

When the time comes to the transmission time (step S24), the informationtransmission control means 3 extracts the specified video program basedon the program identifying data included in the transmission requestdemand and transmission format from the video server 21 in the case ofthe transmission rate of 4 M bits/sec or from the tape informationlibrary system 22 in the case of the transmission rate of 45 M bits/sec,and transmits it (step S25). After completion of the transmission,charging for the transmission is performed (step S26).

If the request time information is determined to be C-class in the stepS12, that is, the transmission request allows delay of a half day to oneday, the transmission planning means 4 finds a free channel from thetransmission plan of the going-down line channels ((“for much delayV.O.D) shown in FIG. 12) assigned to the midnight time zone, and decidesa transmission time so as to transmit by way of the free channel (stepS22).

Then, in the same way as for B-class demands, the transmission planningmeans 4 informs the information transmission control means 3 of the freechannel to be used for the transmission, transmission time, andabove-mentioned analysis result, and notifies the charging means 7 ofthe information on the transmission time. Further, the transmissionplanning means 4 analyzes the transmission format information includedin the demand signal and random access information, and gives theanalysis result to the information transmission control means 3.

The information transmission control means 3 transmits beforehand thefree channel, transmission time (starting time and ending time),transmission format (4 M bits/sec transmission rate or 45 M bits/sectransmission rate), and random access information to the subscriber whosent the demand and is specified by the user ID as the going-downcontrol data having the user ID header information (step S23), and whenthe time comes to the transmission time (step S24), the informationtransmission control means 3 extracts the specified video program basedon the program identifying data included in the transmission requestdemand and transmission format from the video server 21 in the case ofthe transmission rate of 4 M bits/sec or from the tape informationlibrary system 22 in the case of the transmission rate of 45 M bits/sec,and transmits it (step S25). After completion of the transmission,charging for the transmission is performed (step S26). Accordingly, theprocessing routine ends.

Receiving processing of a control data and transmission data in asubscriber terminal

FIG. 16 is a flowchart of a processing routine performed when theterminal controller 320 of a subscriber terminal receives going-downcontrol data and transmission digital data.

The subscriber terminal receives control data of the transmission planaddressed to the demand subscriber terminal referring to the user ID inthe going-down control data from the going-down line Cd (step S31),analyzes it (step S32), and judges whether it requires the immediatereal-time transmission referring to the analysis result (step S33). Thejudgment may be based on, for example, no inclusion of transmission timedata in the going-down control data. Alternately, class information or aflag which indicates whether it requires the real-time transmission isincluded in the going-down control data, and the judgment may beperformed based on the class information or flag.

When the determination result based on the analysis indicates real-timeinformation transmission, it is determined whether the authenticationinformation for copying permission is received (step S34). If theauthentication information is received, the copying enabled conversionmeans 15 operates to control the digital television decoding circuit 319in order to remove copying prohibition processing (step S35).

According to the results of the analysis in step S32, the terminalcontroller 320 detects a transmission channel, supplies a select signalto the frequency conversion circuit 308 to convert the going-downdigital transmission data of the transmission channel to data having afrequency band which can be demodulated, switches the switch circuit 318so as to select 4 M bits/sec data from the de-multiplexing circuit 317,and switches the switch circuit 15 so as to select the television signalfrom the digital television decoding circuit 319 to supply it to atelevision set through the output terminal 316 (step S36). Copyingprohibition processing is removed from the video signal in this case,and so the signal can be copied.

When, as a result of the determination in step S34, it is determinedthat the authentication information for copying permission is notreceived, the process bypasses step S35 and proceeds to step S36, inwhich transmission information is received in real time to supply theinformation to the television set, then the receiving processing routineends. Copying prohibition processing is still applied to the videosignal in this case.

If the determination result in the step S33 does not show an immediatereal-time transmission, then the terminal controller 320 recognizes thetransmission time, transmission channel, transmission format, and randomaccess information based on the analysis result of the above-mentionedgoing-down control data, and prepares for receiving (step S37). Theterminal controller 320 waits for the transmission time of thetransmission information (step S38), and when the time comes to thetransmission time, the terminal controller 320 supplies a select signalfor converting the going-down digital transmission data of thetransmission channel to data having a frequency band which can bedemodulated to the frequency conversion circuit 308, and starts toreceive the digital transmission data according to the transmissionformat (step S39).

Further, any one medium to be used for storing the transmissioninformation is selected previously from the semiconductor memory, harddisk, data streamer, and digital VTR in the temporary memory device 330according to the transmission format included in the going-down controldata and random access information (step S40), and the receivedtransmission information is stored in the selected temporary memorydevice based on the memory permission information which is going-downdata to be sent prior to transmission information, then the receivingprocessing routine ends.

The cable television station HE stores the history of the programstransmitted to each subscriber which, as described later, is used forreferences when the subscribers send reading requests to the cabletelevision station HE.

In this case, if the transmission format specifies high speedtransmission and the semiconductor memory is selected as the temporarymemory means, the transmission information is transmitted with the highspeed transmission rate of 45 M bits/sec, and the transmission data isstored in the semiconductor memory 331 which serves as the temporarymemory means as its high speed transmission rate.

For example, if the transmission rate of compressed digital data is 1.5M bits/sec and a program is a two-hour program, the program compressedto 45 M bits/sec rate is transmitted, then the transmission requiresonly about 4 minutes, and alternately if the transmission rate is 4 Mbits/sec, the transmission of a two-hour program requires only about 11minutes.

In the case that the transmission data rate is 4 M bits/sec due to thetransmission format, the selection of a temporary memory means dependson random access, and the hard disk device is selected for high randomaccess and the data streamer device 333 is selected for low randomaccess as the temporary memory means.

A high fee may be applied to the request for low rate formattransmission in real-time, on the other hand a, low fee may be appliedto the request for high speed rate because the transmission time isshort.

As described herein above, the receiving processing of the transmissioninformation is performed in a subscriber terminal. The television signalreceived in real-time transmission is supplied to a television withoutstoring in the temporary memory device. Therefore, a user can view theprogram with a slight delay.

On the other hand, the video data stored in the temporary memory device330 is reproduced at an arbitrary time and provided to the subscriber inresponse to a reading request (reproduction request) from the subscriberthrough the user interface 321. FIG. 17 shows a flowchart of an exampleof the reproduction processing routine.

For the case that a plurality of video programs is registered in thetemporary memory device due to a plurality of demands, in this example,the terminal controller 320 of a subscriber terminal ms is provided witha function to display the menu of accumulated video programs on thetelevision monitor, the user can select and view any program from themenu.

The terminal controller 320 stores program identification data of eachtransmission program (called program IDs hereinafter) and memory devicesin which the transmission programs are stored, between which acorrespondence has been established.

When a subscriber specifies the program transmitted after delay via theuser interface 321 and inputs a reproduction request including a copyingpermission request as the need arises, the routine in FIG. 17 starts,and in step S51, the user's reproduction request is accepted. Next, theprocess proceeds to step S52, in which it is determined whether thecopying permission request is included in the user's reproductionrequest.

When it is determined that the copying permission request is included inthe user's reproduction request in step S52, the process proceeds tostep S53, whereby the reproduction request command including a user ID,the program ID of a program selected by the user from the informationstored in the temporary memory device 330, and the copying permissionrequest are sent to the cable television station HE through the going-upline.

The process proceeds from step S53 to step S54 and waits for theauthentication information for the copying permission to be receivedfrom the cable television station HE. When it is confirmed that theauthentication information for the copying permission is received instep S54, the process proceeds to step S55, in which the copying enabledconversion means of the digital television signal decoding circuit 319is made operable. Then, the process proceeds to step S57 and waits forthe reproduction start control signal (including a program ID) to bereceived from the cable television station HE.

When it is determined that the copying permission request is notincluded in the user's reproduction request in step S52, the processproceeds to step S56, whereby the reproduction request command includingthe user ID and the program ID of the program specified by the user andexcluding the copying permission request is sent to the cable televisionstation HE through the going-up line. After the step S56, the processproceeds to step S57 and waits for the reproduction start control signalto be received from the cable television station HE.

When it is confirmed that the reproduction start control signal isreceived from the cable television station HE in step S57, the processproceeds to step S58, in which the terminal controller 320 reproduces(reads) the program information identified with the above-mentionedprogram ID from the medium of the temporary memory device 330 in whichthe program information specified with the program ID is stored.

Upon receiving the reproduction instruction, the temporary memory devicereads the corresponding digital video data of the program, and suppliesit to the digital television decoding circuit 319 through the switchcircuit 318. In this case, the rate of the read digital data is 4 Mbits/sec. The video signal from the decoding circuit 319 is supplied toa television through the output terminal 316, and provided to the user.

When information copying is permitted, the video signal from the outputterminal 316 can be recorded in VTR or suchlike.

Then, the process proceeds to step S59 and waits for the reproductionend instruction to be received through the user interface 321 of thesubscriber. When the reproduction end instruction is confirmed in stepS59, the process proceeds to step S60, in which a deletion requestincluding the user ID and program ID are sent to the cable televisionstation HE through the going-up line. When the deletion instructioncontrol signal is received from the cable television station HE in stepS61, the process proceeds to step S62, in which the used transmissionprogram is deleted from the above-mentioned temporary memory device,then the reproduction processing routine ends.

Next, an example of receiving a production request from the subscriberis described referencing the flowchart in FIG. 18.

The processing routine in FIG. 18 starts when the cable televisionstation HE receives a reproduction request from the subscriber, and theproduction request is accepted in step S71. Next, the process proceedsto step S72, in which it is determined by a program ID whether theprogram has really been transmitted or whether the program should havealready been deleted. In this case, as described above, since the cabletelevision station HE retains the history of the transmitted programsfor each user ID, the determination processing is performed referencingthe retained information.

When it is determined that the program has not been transmitted yet orshould already have been deleted in step S72, the processing routineends.

When it is determined that the program has been transmitted and has notyet been deleted in step S72, the process proceeds to step S73, in whichit is determined whether the copying request is made. When the copyingrequest is already made, the process proceeds to step S74, in which theauthentication information for the copying permission is fetched fromthe data base 8 and the fetched information as going-down control datais sent to the subscriber who made the copying request. In the next stepS75, an additional fee for the copying permission is charged for thecorresponding subscriber.

Next, the process proceeds to step S76, in which the reproduction startcontrol signal specifying a program to be reproduced with a program IDis sent to the subscriber who made the reproduction request. Thus, thereproduction request receiving processing ends.

When the deletion request including a user ID and a program ID isreceived from the subscriber, as described above, the cable televisionstation HE sends the deletion control signal to the correspondingsubscriber.

In the above example, the user makes a request for the permission ofcopying a program to be transmitted after delay at the same time whenthe user makes a request for reproducing the program. However, thecopying permission request may be included in a program. When the useralready made the copying permission request, transmission ends. In thiscase, when the user makes a request for reproducing the transmittedprogram, the cable television station determines whether the user makesa copying permission request during the program demand. The cabletelevision station sends the authentication information for the copyingpermission to the user before the reproduction start control signal.

Further, in case of making a copying permission request during such ademand, the instruction of whether the user wants to use the sameprogram again is included in the reproduction end instruction. After thereproduction end instruction is confirmed, it is determined whether thereusing request is made. When no reusing request is made, the usedtransmission program is deleted from the above-mentioned temporarymemory device. When it is determined that a reusing request is made, theused transmission program is not deleted, and the reproductionprocessing routine is terminated, thus enabling the use of the sameprogram more times than once. In this case, an additional fee is chargedfor the copying permission whenever the program is reproduced.

Since consideration is given to copying in the above example, thedeletion instruction is issued before instructions to be issued by thecable television station. In the system in which copying is impossible,however, reproduction is performed at the subscriber terminal, and itmay be specified that, after a program is used, the program can bedeleted without failure only under the control by of subscriberterminal.

In the first embodiment described herein above, a user can demand notonly the immediate real-time transmission but also the delayedtransmission, therefore, a user who wants to view the program in theprime time zone can demand for the program to be transmitted during themidnight time zone and the program will be stored in the temporarymemory device, and the user can view the demanded program at the desiredtime.

The above-mentioned demand-delayed view system favors the demand forimmediate real-time transmission in prime time to decrease.

Since demands are classified into various types according to the classeswhich indicate the urgency of information transmission, and, forexample, since the lower fee for the demand allowable of delayedtransmission than that for the demand for immediate real-timetransmission is applied according to the delay time length, such feesystem favors the demand in prime time to decrease.

Such suppressed generation of the immediate real-time transmission inprime time allows the cable television station to be provided with asmaller scale facility in comparison with the conventional cabletelevision station which transmits programs only in real-time.

Transmission capacity of going-down digital transmission data isallocated to an independent plurality of transmission channels dependingon the information relating to the class which indicates the urgency ofinformation transmission in the demand and many channels are allocatedto the immediate real-time transmission in prime time. On the otherhand, many channels are allocated to the delayed transmission inmidnight, and such change of allocation depending on the time zoneallows the transmission capacity to be used efficiently.

In the above-mentioned embodiment, high speed transmission is possiblefor delayed transmission in comparison with real-time transmission, andthe time required for transmission of one program is shortened incomparison with the conventional method and, in this aspect also, thetransmission capacity is used efficiently. Accordingly, charges for thesubscriber can be reduced to low rates, and it is expected that the wideuse of the video on-demand systems is promoted.

In the above-mentioned first embodiment, allocation of the number oftransmission channels depending on the information relating to theurgency class of the demand is changed in the time zone of a day, butthe allocation may be changed dependently on days in a week, or may bechanged in combination of time zone and week.

After the transmission program is used, the program stored in thesubscriber terminal is automatically deleted, thus enabling the sureprotection of the copyright of the program. In addition, since anadditional special fee is charged for program copying, effectivecopyright protection can be expected.

Example of change

In the above-mentioned first embodiment, the allocation of transmissionchannels depending on the information relating to the urgency class ofthe demand is changed within only the transmission capacity of thegoing-down digital information data, but, because the audience rate ofanalog television broadcast decreases, the transmission band of analogtelevision broadcast is reduced and the reduced transmission band isused as the transmission band of digital information data.

In this case, a program table including channel assignment differentbetween prime time and midnight is prepared for analog televisionbroadcast, and this program table is transmitted to subscriberspreviously to inform them of the change of program channels depending onthe time zone.

A plurality of data compression systems for digital transmission data isprovided in the cable television station, for example, depending on arequested degree of resolution, and any one of the data compressionsystems may be selected by way of the demand from a subscriber terminal.In this case, a plurality of decoders are provided in a subscriberterminal depending on the above-mentioned plurality of data compressionsystems, and the information including compression system information inthe going-down control data from the television station is sent to thesubscriber terminal, and the decoder is switched dependently on thecompression system information.

In this case, the compression rate is low and the amount of data islarge, but the charges for high-resolution and high-quality videoprogram transmission are specified as high in consideration of the longtransmission time. On the other hand, for a high compression rate, asmall data amount, and short transmission time, the charges can bespecified as low.

In the above-mentioned embodiment, a B-class demand is storednecessarily in the temporary memory means, but because it is possible todisplay the transmission time sent from the station on a display of asubscriber terminal and to inform a user, a mode for specifyingreal-time transmission reproduction for a B-class demand without storingin the temporary memory means may be provided.

Further in the above-mentioned embodiment, the temporary memory means isselected based on the transmission format and random access relatinginformation in the going-down control data in a subscriber terminal, butalternately a demand signal sent from a subscriber terminal is stored inthe subscriber terminal, and the temporary memory means may be selectedfor the transmitted transmission data depending on the stored demandsignal. In this case, an identification data ID for identifying thedemand signal may be added to the demand signal to judge the demand. Inthis case, the information relating to the transmission format andrandom access is not necessarily included in the going-down controldata.

Second embodiment

The second embodiment shows an example in which an existing CATV cablenetwork is used. In a conventional CATV cable network, a cabletelevision station is connected to a plurality of subscriber terminalsby way of coaxial cable, and provides mainly analog television broadcastto each subscriber terminal by way of coaxial cable.

In the second embodiment, a facility for transmission of digital datasuch as video data is added to a cable television station without achange of the conventional transmission line facility using coaxialcable, and a receiving unit for receiving digital data provided with alarge capacity temporary memory device is added to a subscriberterminal. The public phone network is used as the going-up line fortransmission of digital data demand.

FIG. 19 shows the whole network structure of the embodiment. In a cabletelevision station 40, an analog television broadcast signal Va from theabove-mentioned analog television broadcast facility 401 and digitaldata Vb such as digital video data from the digital transmission datatransmission facility 402 are synthesized to generate a frequencymultiplexed signal, and sent to the coaxial cable CB through anamplifier 404.

A plurality of telephone lines L1 to Ln are connected to the publicphone network PSTN, and a station side controller 405 for receivingdemands from subscribers through the telephone lines L1 to Ln and forsending video programs corresponding to the demand from the digital datatransmission facility 402 are provided.

Also in this embodiment, the station side controller 405 generatesgoing-down control data Vc including a user ID for specifying theaddressed subscriber terminal which receives the digital data, programID, transmission channel, and transmission time information in order tosend the digital data to the subscriber terminal which transmitted thedemand, and supplies it to a synthesizer 403 to frequency-multiplex theinformation for transmission of the going-down control data Vc, andsends it to a subscriber terminal.

FIG. 20 shows the frequency assignment of a frequency multiplexed signalfor transmitting in the coaxial cable CB, whereby a 50 MHz to 450 MHzfrequency band is used for analog television broadcast signals as it isused conventionally. The frequency band around 500 MHz is used for thegoing-down control data having a transmission rate of 1.5 M bits/sec asit is used in the above-mentioned embodiment. Two frequency bands of ahigher frequency are used for transmission of the going-down digitaldata having a transmission rate of 45 M bits/sec. In other words, twochannels are assigned to digital data.

Subscriber terminals 50 are connected to the coaxial cable CB throughcoaxial confluent distributors 60 as it is so connected in the sectionalnetwork in the above-mentioned embodiment. The coaxial confluentdistributor 60 comprises an input buffer amplifier 61 for receivinginformation from the coaxial cable CB connected to the coaxial confluentdistributor connected in front, a distributor 62 for identifying thesignal between a signal to be distributed to the subscriber terminalconnected to the coaxial confluent distributor and a signal to bedistributed to subscriber terminals in the down stream, and an outputbuffer amplifier 63 for supplying an output signal to subscriberterminals in the down stream.

A subscriber terminal 50 is connected to the public phone network PSTNthrough a telephone line Lms as shown in FIG. 19. A telephone 70 isconnected to the telephone line Lms through the subscriber terminal 50,and a television 80 is connected to the subscriber terminal 50.

The cable television station 40 has in detail, for example, a structureshown in a block diagram of FIG. 21. In detail, an analog televisionbroadcast signal Va is subjected to band restriction to generate asignal of the band for the above-mentioned analog television broadcastthrough a band pass filter 411, and thereafter is sent to a synthesiscircuit 403.

The digital transmission data transmission facility is provided with atape information library system 402. The tape information library system402 comprises a tape container rack 412L, a plurality of players VTRa toVTRd, a transferring mechanism (not shown in the figure) for taking outa desired cassette tape from the tape container rack and for charging itto any one of the players VTRa to VTRd as it is so structured in theabove-mentioned embodiment. But in this second embodiment, two playersVTR are provided for each channel, that is, a total of four playersVTRa, VTRb, VTRc, and VTRd are provided, so that the facility issimplified in comparison with the tape information library system of theabove-mentioned cable television station HE having the digital facility.

The station side controller 405 controls the selection of a channel outof the two channels and decides the selection of a player out of the twoplayers by switching and controlling switch circuits 413 and 414. Likethe prescribed first embodiment, charging is performed. In detail,different charges are specified according to the urgency oftransmission, transmission time, and data compression rate, whereby highrates are charged for urgent transmission and transmission in a timezone of much traffic such as prime time and for a low data compressionrate. An additional fee is charged for the permission of copying.

Digital data from respective switches 413 and 414 is modulated inhexternal QAM modulation circuits 415 and 416 as it is so modulated inthe above-mentioned embodiment, and subsequently supplied to thefrequency conversion circuits 417 and 418, and frequency-converted to asignal of the band for each channel shown in FIG. 16. The output signalof the frequency conversion circuits 417 and 418 is supplied to thesynthesis circuit 403.

Going-down control data Vc from the station side controller 405 issupplied to a QPSK modulation circuit 419 and modulated, thenfrequency-converted to a signal of the band for control data shown inFIG. 18. The output signal from the frequency conversion circuit 420 issupplied to the synthesis circuit 403.

Going-up demand data sent from a subscriber terminal through thetelephone lines LI to Ln is taken in the station side controller 405through modulators 421 to 42n. The going-down control data Vc isgenerated based on the going-up demand data. The demand data includes auser ID for identifying the subscriber terminal, data for identifyingthe requested program, and request time information describedhereinafter. The demand data sometime includes a copying permissionrequest.

Next, a subscriber terminal has a structure, for example, shown indetail in a block diagram of FIG. 22.

The going-down signal from the coaxial confluent distributor 60 issupplied to band pass filters 502 and 503 through an input terminal 501.The band pass filter 502 has a pass band of the analog televisionbroadcast signal frequency band shown in FIG. 18, and the analogtelevision signal obtained from the band pass filter 502 is supplied toa frequency conversion circuit 504.

The channel selection control signal corresponding to the channelselection operation through the user interface 530 from the terminalcontroller 520 is supplied to the frequency conversion circuit 504, andthe analog broadcast program channel signal selected by a user isconverted by the frequency conversion circuit 504 to a signal of afrequency which can be demodulated by the subsequent analog televisiondemodulation circuit 505. The output signal from the frequencyconversion circuit 504 is supplied to the analog television demodulationcircuit 505, and the television signal of the above-mentioned selectedanalog television broadcast program channel is demodulated. Thedemodulated television signal is supplied to an output terminal 507through a switch circuit 506.

A television 70 is connected to the output terminal 507. A userinterface 530 comprises a remote controller and key board device as itso comprises in the above-mentioned embodiment.

The going-down control data and going-down digital information data areobtained from the band pass filter 503. The going-down control data isconverted by a frequency conversion circuit 512 to a signal of a bandwhich can be demodulated by the subsequent QPSK demodulation circuit513, and then supplied to a QPSK demodulation circuit 513 anddemodulated. The demodulated control data is supplied to ade-multiplexing circuit 514, and only the control data of the channelgiven to the demand subscriber terminal by the control signal from theterminal controller 520 is taken out, and supplied to the terminalcontroller 520.

The terminal controller 520 interprets the control data, judges whetherthe control data is addressed to the demand subscriber terminal based onthe user ID included in the control data, and if the control data isaddressed to the demand subscriber terminal, the terminal controller 520analyzes the control data and is informed of the above-mentioned programID, transmission time, and transmission channel (out of the digital datatransmission channels).

The digital information data from the band pass filter 503 is suppliedto a frequency conversion circuit 508. In the frequency conversioncircuit 508, only the information data of the transmission channel foundby analyzing the above-mentioned control data is converted to a signalof a frequency which can be demodulated by a hexternal QAM demodulator509 based on the control signal from the terminal controller 520. Theoutput signal from the frequency conversion circuit 508 is supplied tothe hexternal QAM demodulation circuit 509 and demodulated, thedemodulated signal is supplied to a data streamer device 510 andtemporarily stored.

The data streamer device 510 has such a structure that a tape mediumcannot be removed from the device. The recording of data in andreproduction from the data streamer device 510 are performed under thecontrol of the cable television station.

In the same way as for the above-mentioned first embodiment, theterminal controller 520 sends the reproduction request to the cabletelevision station 40 in response to the reproduction request inputincluding the program ID through the user interface 530 of the user.When the terminal controller 520 receives a reproduction start controlsignal from the cable television station 40, the controller 520 issues areproduction instruction including the program ID to the data streamer510. The data streamer device 510 reads and regenerates the digitalinformation specified by the program ID out of temporarily storedinformation in response to the reproduction instruction.

The read digital information is subjected to error correction decodeprocessing in a digital television signal decoding circuit 511,converted to an analog television signal, and supplied to the switchcircuit 506.

When a copying request is included in a reproduction request, thecopying enabled conversion means of the digital television signaldecoding circuit 511 is made operable, and the digital television signaldecoding circuit 511 outputs the signal from which copying prohibitionprocessing is removed in the same way as for the above-mentioned firstembodiment.

The switch circuit 506 is switched to the analog television signaldemodulation circuit 505 side during analog television broadcast forreceiving channel selection or to the digital television signal decodingcircuit 511 side when watching the temporarily stored programdependenting on the switching signal from the terminal controller 520 inresponse to the user input through the user interface 530, and the usercan view the respective programs in the television connected to theoutput terminal 507. When the user's program viewing ends, that is,program reproduction ends, the corresponding program is deleted from thedata streamer 510 in the same manner as for the above-mentioned firstembodiment.

The terminal controller 520 generates a demand signal as going-up datain response to a demand input for a digital information program throughthe user interface 530. The demand signal includes the user ID, ID ofthe demanded program, and request time information of the urgency forthe demanded program as included in the above-mentioned embodiment. Ifthe same plurality of compression methods as used for digitaltransmission of a video signal transmitted from the cable televisionstation side is provided and a user can select the compression methoddepending on the demanded information and necessary resolution, then thedemand signal includes the transmission format such as a datacompression ratio. As described above, a request for copying may beincluded in the demand signal.

The demand signal from the subscriber terminal is modulated by amodulator 521, and sent out to the telephone line Lms connected to thepublic telephone network through NCU (network control unit) 522. Atelephone 70 is connected to NCU 522 through the telephone terminal 524,and the telephone 70 is used as it is used usually.

In the second embodiment, the cable television station 40 accepts onlytransmission requests for delay allowable demands corresponding toB-class and C-class demands in the above-mentioned first embodiment. Inmore detail, real-time transmission and digital television broadcast arenot involved, so that two-way information transmission is realized onlywith adding some additional facility to the existing cable televisionsystem facility.

In this embodiment, when a user inputs a demand to the subscriberterminal, the user selects request time information which is either aB-class demand allowable of little delay or a C-class demand allowableof a delay of a half day to one day.

Upon receiving the demand from the user through the public telephonenetwork PSTN, the cable television station 40 plans a transmission planso as to transmit successively requested programs if the demand isB-class. In detail, if there is a free channel in the going-down digitalinformation data band, the cable television station 40 plans thetransmission plan so as to transmit the demanded program information tothe subscriber terminal by way of the free channel.

Upon completion of the transmission plan, the cable television station40 transmits beforehand going-down information including the time whenthe requested program is to be transmitted, the channel to be used forthe transmission, and the going-down control data including transmissionformat information to the subscriber terminal which transmitted thedemand through a control data transmission channel. As described above,charging is performed according to A- to C-class demands andtransmission time zones.

The subscriber terminal 50 acquires the control data addressed to thedemand subscriber terminal, and is informed previously of the time fortransmission, channel to be used for the transmission, and transmissionformat, and prepares for receiving. Monitoring the time for finding thetransmission time, the subscriber terminal 50 receives the digitalinformation data transmitted with address to the demand subscriberterminal 50 through the above-mentioned band pass filter 503, frequencyconversion circuit 508, and hexternal QAM demodulation circuit 509, andstores the received digital information data in the data streamer device510.

When the user inputs at an arbitrary time a reproduction request for theselected specified program out of temporarily stored programs throughthe user interface 530, the terminal controller 520, as described above,sends the reproduction request to the cable television station 40 andwaits for a reproduction start control signal to be incoming. When thereproduction start control signal is incoming, the terminal controller520 sends a reproduction instruction of the specified program to thedata streamer device 510. The data streamer device 510 reads andregenerates the specified program in response to the reproductioninstruction, and supplies the television signal to the televisionthrough the output terminal 507, and the user can view the program. Whenthe user's program viewing ends, the corresponding program isautomatically deleted.

In the second embodiment, processing and charging are performed for thepermission for copying a transmitted program in the same way as for thefirst embodiment.

As described herein above, in the case of the second embodiment, thereal-time transmission is not necessary, the introduction of a largescale system such as video server is not necessary, the video on-demandsystem is realized with a relatively small investment, the digitalinformation data can be transmitted with a delay efficiently during thetime zone such as midnight when traffic is infrequent, and thus thetransmission band can be used efficiently.

A demand signal is sent to the television station through the publictelephone network, therefore it is unnecessary to provide an extratransmission line for going-up data and, thus extra investment for thispurpose is not necessary.

The application of this invention to the video on-demand system isdescribed hereinbefore, however, the present invention can be applied tonot only a video system but also other two-way information transmissionsystems which transmit various information in response to a demand.

In the above embodiment, deleting information from the memory is used asthe means for disabling the reusing of the information. In addition,such a method may also be used that a specified noise is written overthe corresponding information to disable the reusing of the information.

As described hereinbefore, according to the present invention, the videoon-demand system can be realized without introduction of large scalesystem such as video server and with relatively small investment. Thecentralization of traffic is mitigated, and the network resource is usedefficiently.

Rational charging can be performed in response to transmission requestsand the wide use of the two-way information transmission systems ispromoted by specifying a low rate for real-time transmission even fordelay transmission.

Moreover, if the subscriber terminal is provided with a memory device,the copyright on the information can be protected effectively.

What is claimed is:
 1. A two-way information transmission systemcomprising: an information distribution transmission center forreceiving an information distribution transmission request and fortransmitting requested information; a plurality of subscriber terminalsconnected to said information distribution transmission center bygoing-up lines and going-down lines for transmitting said informationdistribution transmission request to said information distributiontransmission center through said going-up lines and for receiving saidrequested information transmitted by said information distributiontransmission center through said going-down lines, wherein each of saidplurality of subscriber terminals includes: distribution transmissionrequest transmitting means for transmitting said informationdistribution transmission request to said information distributiontransmission center having at least information for identifying one ofsaid plurality of subscriber terminals transmitting said informationdistribution transmission request, information for identifying saidrequested information, and information relating to an urgency of saidrequested information, memory means for storing said requestedinformation transmitted by said information distribution transmissioncenter, transmission plan receiving analysis means for receiving atransmission plan based on going-down control data from said informationdistribution transmission center, information acquisition means forreceiving the requested information transmitted by said informationdistribution transmission center based on said transmission plan and forstoring the requested information in said memory means according to theurgency of said requested information based on said transmission plan,reading means for reading the requested information from said memorymeans, and information reuse disabling means for disabling reusing ofthe requested information read from said memory means by said readingmeans, and wherein said information distribution transmission centerincludes: transmission planning means for planning a transmission planfor transmitting the requested information based on said informationdistribution transmission request from one of said plurality ofsubscriber terminals, transmission implementation means for transmittingsaid requested information based on the transmission plan planned bysaid transmission planning means to one of said plurality of subscriberterminals, and going-down control data sending means for sending saidgoing-down control data including information of the transmission planplanned by said transmission planning means to one of the plurality ofsubscriber terminals which sent said information distributiontransmission request before said transmission implementation meanstransmits the requested information.
 2. The two-way informationtransmission system as claimed in claim 1, wherein said memory meansincludes a mechanism that prevents a memory medium from being directlyremoved from each of said plurality of subscriber terminals.
 3. Thetwo-way information transmission system as claimed in claim 1, whereinauthentification information for permitting copying of transmittedinformation is transmitted from said information distributiontransmission center to said plurality of subscriber terminals inrelation to said information distribution transmission requests andwherein said information acquisition means of said plurality ofsubscriber terminals stores said requested information in said memorymeans based on said authentification information.
 4. The two-wayinformation transmission system as claimed in claim 1, wherein, aftersaid requested information is read from said memory means, saidinformation reusing disabling means automatically performs one ofdeleting the requested information from said memory means and logicallywriting information in the memory means over the read out requestedinformation.
 5. The two-way information transmission system as claimedin claim 1, wherein each of said plurality of subscriber terminalsfurther includes: a user interface for a user to input a memory readingrequest for reading said requested information from said memory means,and means for transmitting the memory reading request to saidinformation distribution transmission center through said going-up linein response to the input of said memory reading request by said user viasaid user interface, wherein said information distribution transmissioncenter sends a reading permission signal from said going-down controldata sending means to one of said plurality of subscriber terminalsthrough said going-down line in response to the memory reading requestinputted by said user from one of said plurality of subscriberterminals.
 6. The two-way information transmission system as claimed inclaim 5, wherein a copying permission request in addition to said memoryreading request is transmitted from one of said plurality of subscriberterminals to said information distribution transmission center throughsaid going-up line, and upon said information distribution transmissioncenter receiving said copying permission request from one of saidplurality of subscriber terminals, said information distributiontransmission center transmits to one of said plurality of subscriberterminals control data for removing copying prohibition from saidrequested information to be read from said memory means, and charges anadditional fee to one of said plurality of subscriber terminals thattransmitted said copying permission request.
 7. A method for two-wayinformation transmission comprising the steps of: transmitting aninformation distribution transmission request from one of a plurality ofsubscriber terminals to an information distribution transmission centerincluding at least information for identifying one of the plurality ofsubscriber terminals that transmitted said information distributiontransmission request, information for identifying requested information,and information relating to an urgency of the requested informationthrough a going-up line; planning a transmission plan by saidinformation distribution transmission center for information to betransmitted based on said information distribution transmission requestfrom one of said plurality of subscriber terminals; and transmittingsaid transmission plan from said information distribution transmissioncenter to one of the plurality of subscriber terminals which transmittedsaid information distribution transmission request in going-down controldata through a going-down line prior to the transmission of therequested information, and thereafter transmitting said requestedinformation through said going-down line according to said transmissionplan, whereby one of said plurality of subscriber terminals is informedof said transmission plan by receiving and analyzing said going-downcontrol data transmitted from said information distribution transmissioncenter, receives the requested information transmitted from saidinformation distribution transmission center based on the acquiredtransmission plan, stores the requested information in a memory having alarge capacity according to the urgency of said requested information,reads said requested information from said memory for using saidrequested information, and after said requested information is used by auser, disables a reusing of the requested information.
 8. A plurality ofsubscriber terminals connected to an information distributiontransmission center through going-up lines and going-down lines forrequesting information from said information distribution transmissioncenter through said going-up lines and for receiving the requestedinformation from said information distribution transmission center inresponse to the request through said going-down lines, each subscriberterminal of said plurality of subscriber terminals comprising:distribution transmission request sending means for transmitting aninformation distribution transmission request to said informationdistribution transmission center including at least information foridentifying one of the plurality of subscriber terminals transmittingsaid information distribution transmission request, information foridentifying requested information, and information relating to anurgency of said requested information; memory means for storing saidrequested information transmitted by said information distributiontransmission center; transmission plan receiving analysis means forreceiving a transmission plan for said requested information to betransmitted by said information distribution transmission center,wherein said transmission plan is based on said information distributiontransmission request transmitted by one of said plurality of subscriberterminals, by referring to going-down control data transmitted by saidinformation distribution transmission center; information acquisitionmeans for receiving the requested information transmitted by saidinformation distribution transmission center based on the transmissionplan and for storing the requested information in said memory meansaccording to the urgency of said requested information based on saidtransmission plan; reading means for reading the requested informationfrom said memory means; and information reusing disabling means fordisabling the reusing of the requested information read from said memorymeans by said reading means and used by a user.